... yet avoids appearance of doing so, by treating ‘consideration’ of the relations of a felt thing as if it were itself the feeling. 253. It is thus by playing fast and loose with the difference between feeling and conception that Hume is able, when the character of extension as an intelligible relation is urged, to reply that it is the same with the feeling of colour; and on the other hand, when asked how there then can be an abstract idea of it, to reply that this does not mean a separate idea, but coloured objects considered under a certain relation, viz. under that which consists in the disposition of their parts. The most effective way of meeting him on his own ground is to ask him how it is, since ‘consideration’ can only mean a succession of ideas, and ideas are fainter impressions, that extension, being one and the same impression with colour, can by any ‘consideration’ become so different from it as to constitute a resemblance to objects that are not coloured at all. The true explanation, according to his own terminology, would be that the resemblance between the white globe and all other globes, being a resemblance not of impressions but of such relations between impressions as do not ‘depend on the nature of the impressions’ related, is unaffected by the presence or absence of colour or any other sensation. Of such relations, however, there can properly, if ideas are fainter impressions, be no ideas at all. In regard to those of cause and identity Hume virtually admits this; but the ‘propensities to feign’ by which in the case of these latter relations he tries to account for the appearance of there being ideas of them, cannot plausibly be applied to relations in space and time, of which, as we shall see, ideas must be assumed in order to account for the ‘fictions’ of body and necessary connexion. Since then they cannot be derived from any separate impression without the introduction in effect of a sixth sense, and since all constitutive action of thought as distinct from feeling is denied by Hume, the only way to save appearances is to treat the order in which a multitude of impressions present themselves as the same with each impression, even though immediately afterwards it may have to be confessed, that it is so independent of the nature of any or all of the impressions as to be the foundation of an abstract idea, which is representative of other impressions having nothing whatever in common with them but the order of appearance. This once allowed--an abstract idea having been somehow arrived at which is not really the copy of any impression--it is easy to argue back from the abstract idea to an impression, and because there is an idea of the composition of points to substitute a ‘composition of coloured points’ for colour as the original impression. From such impression, being already extension, the idea of extension can undoubtedly be abstracted. Summary of contradictions in his account of extension.